If I have web forms hosted in various sites, how can I track where the leads are coming from?

You can track the source of your leads by adding a hidden field in your web forms and giving a unique value for the hidden field.

In the web form editor, drag and drop a desired field and make it a hidden field. Let us consider the Lead Source field for example.

Drag and drop the Lead Source field in the Editor.

Click the Settings tool.

Select the Mark as hidden field check box.

Enter a default value for each form.

For Site 1 you could say Website. For a form on Site 2 you could select the default value as blog or any other appropriate option. When you publish the form, this field will not be visible to the users but the default value will be submitted along with other details when the forms are submitted.

So you can keep a track of where the leads are coming from by using the default value assigned to the hidden field.